UMTS PS Service Analysis
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Transcript of UMTS PS Service Analysis
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UMTS PS Service Analysis
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Contents
1 PS Service Data Transmission Analysis Method ........................................................................... 1
1.1 Data Collection .................................................................................................................. 1
1.1.1 DT/CQT Data Collection........................................................................................... 2
1.1.2 Collection of Other Data............................................................................................ 3
1.2 Data Analys is Method......................................................................................................... 4
1.2.1 Common Problem Analysis Method ............................................................................ 4
1.2.2 Typical NE Locating Method ..................................................................................... 6
2 Data Analysis ............................................................................................................................. 9
2.1 Basic Problem Analysis ...................................................................................................... 9
2.1.1 Access Failure.......................................................................................................... 9
2.1.2 No Traffic flow on the User Plane..............................................................................17
2.2 Problems of Data Transmission Performance ........................................................................26
2.2.1 Checking the Alarms................................................................................................28
2.2.2 Factors Affecting the Data Transmission at the lub Interface .........................................29
2.2.3 Comparison and Analysis of Operation Type ...............................................................30
2.2.4 R99 Problem...........................................................................................................32
2.2.5 HSDPA Analysis........................................................................................................38
2.2.6 Poor Data Transmission Performance at CN Side.........................................................59
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1 PS Service Data Transmission Analysis Method
The upper layer of PS services includes FTP and HTTP services etc. Most services are
established over TCP protocol which is a reliable transmission protocol and
retransmission may occur. Retransmission will have great impact on the rate. If
parameters are improperly configured or packets are wrong or lost during the
transmission, data transmission rate will also be affected. The service quality can be
estimated by using the UE as the Modem, i.e. using UE + PC to dial. Therefore the
performance of the computer and server may also affect the data transmission. In this
case, first confirm whether the problem is caused by the network or other. Usually
methods such as exclusion, separation, and packet capture are used to locate and solve
the problem.
1.1 Data Collection
SGSN/GGSN
RNC
Node BUE
Server
Figure 1-1 End-to-end data transmission process
As shown in the above figure, data transmission optimization involves multiple NEs.
Therefore collecting complete information at different interfaces is important for
optimization and problem location. Data collection mainly includes OMC traffic
statistics collection, DT data collection, background tracking of NEs and end-to-end
data capture on the user plane. The most commonly used DT tools are ZTE CNT
network optimization tool, Qualcomm QXDM software and their corresponding
background analyzing tools of CNA and QCAT (APEX).
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1.1.1 DT/CQT Data Collection
Currently the DT/CQT is usually carried out using CNT and QXDM software
(connected to the UE, Scanner or GPS). Thus information such as pilot coverage,
signaling f low, DL BLER and UE transmission power can be obtained. Combining
with measurement tracking of users in OMC-R, UL BLER, DL code field transmission
power, UL receiving power and signaling flow at RNC side can be acquired. Use
CNA/QXTM/DT processing software to make comprehensive analysis based on data
collected by CNT, QXTM, and tracking record in OMC-R operation and maintenance
console.
Note: Time synchronization should be performed before data collection.
Information that should be collected is shown in the following table:
Table 1-1 Main Parameters that Should Be Collected through DT/CQT
Parameter Method Function
Geographic information
(longitude and latitude) CNT+GPS Record the track
Scrambling code, RSCP, Ec/Io of
cells in the active set CNT+UE Analyze the problem
UE Tx Power CNT+UE or QXDM+UE Analyze the problem and
export the report
UL BLER CNT+UE or QXDM+UE Analyze the problem and
export the report
Throughput in UL/DL application
layer and in RLC layer CNT+UE or QXDM+UE
Analyze the problem and
export the report
RRC, NAS signaling at UE side CNT+UE or QXDM+UE Analyze the problem
HSDPA CQI, HS-SCCH
scheduling success rate,
throughput at APP, RLC, MAC
layers.
QXDM+UE Analyze the problem and
export the report
HSUPA average SG, DTX%,
throughput at layers of APP, RLC
and MAC
QXDM+UE Analyze the problem and
export the report
UL BLER OMC-R Analyze the problem and
export the report
Tx code power OMC-R Analyze the problem and
export the report
RNC single user signaling OMC-R Analyze the problem
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Chapter 1 PS Service Data Transmission Analysis Method
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Parameter Method Function
tracing
Iub bandwidth OMC-B Analyze the problem
DL carrier transmission power
and non-HSDPA carrier
transmission power
OMC-R Analyze the problem and
export the report
DL throughput and bandwidth OMC-R Analyze the problem and
export the report
DL traffic volume OMC-R Analyze the problem
1.1.2 Collection of Other Data
Traffic statistics, DT/CQT and user complaints help to find faults. Apart from traffic
statistics and DT/CQT, other tools and their functions can be combined to analyze and
locate faults. Functions such as connection performance measurement and cell
performance measurement of RNC background tracking, alarm query, and status query
of NEs, and tools such as FlashGet, DU Meter can all help to locate faults. In PS
service test, to reduce the effect brought by TCP receive window of the application
layer, multi-thread downloading tool such as FlashGet is recommended and the thread
count is generally set to 5. For UL data transmission, multiple FTP processes can be
used for uploading.
Table 1-2 Data that Should Be Collected
Data Data collection
tool
Data
viewing/analyz
ing tool
Function Remark
Traffic statistics OMCR CNO
From macroscopic aspect,
monitor the network
running status and analyze
whether there is fault in the
network, and which NE has
faults.
DT/CQT testing
data
QXDM+UE/C
NT+UE QCAT/CNA Combining DT/CQT
measuring data and RNC
tracing data, make analysis
from the perspectives of call
process and coverage etc.
Connectivity
measurement,
cell
performance
OMCR
OMCR/
analysis
1.22.26/signali
ngCalDateRa
Refer to online
help on RNC O
& M console.
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UMTS PS Service Analysis
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Data Data collection
tool
Data
viewing/analyz
ing tool
Function Remark
measurement
and RNC
signaling
tracing
e/runsignal
UESigStat
Alarms OMCR(OMC
B)
OMCR(OMC
B)
View the alarms and find
the abnormal NE.
Association log
Association
logs at RNC
background
Association
logs at RNC
background
It records abnormal call
history of all users, and
helps to locate the
Problem. Especially for
users complaints, the
problem can be located
through the analysis of
The association logs.
Upload or
download
software
FlashGet etc. null
Multi-thread downloading
to get the stable throughput
rate.
PS service test
assisted tool.
Rate monitoring
software DU Meter null
Make real-time monitoring
of the throughput rate of the
application layer, and record
total throughput, average
throughput rate and peak
throughput rate (the result
can only be recorded
through screenshots).
PS service test
assisted tool.
1.2 Data Analysis Method
1.2.1 Common Problem Analysis Method
When problems occur, make tracing of relevant equipment to make the problem recur,
and get the relevant information:
1. Collect configuration and alarm information of relevant equipment. If necessary,
get the traffic statistics of important tasks. Judge whether packets are lost and
retransmitted based on the existing information. Analyze whether there is data
transmission in the uplink and no data transmission in the downlink at SGSN side
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Chapter 1 PS Service Data Transmission Analysis Method
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or whether there is great delay based on user tracing in SGSN. If the UE cant be
located, use packet capture and exclusive methods to locate the problem.
2. PS data transmission problem mainly includes blocked data transmission,
interrupted data transmission and low data transmission rate. The universal
approach is to make tracing of related UEs or make packet capture at UE
interfaces so as to locate the problem.
3. Take low rate problem for example, it is typical and hard to be located. The
problem usually occurs when the PC accesses the network through the UE to
perform the FTP download or VOD services etc. The procedures to locate the
problem are shown below:
i. Start user tracing in the SGSN and GGSN (if the RNC has this function, initiate
the CDR function) and monitor and eliminate obvious faults in signaling plane
and user plane. Run packet capture tool (for example, Ethereal) in the PC
(connected to the UE), Gi interface or the server.
ii. After the service is stopped, analyze the captured PPP packets at Gi interface and
UE side. Monitor the UL and DL data flow and confirm whether there is packets
loss, retransmission, or out-of-order etc, which affects the rate. By data flow
comparison at different interfaces, judge which part brings the problem. (Use a
relevant tool to converts data packets of SGSN user tracing \ to files which can be
analyzed by Ethereal using a relevant tool. Refer to Commissioning Guide on
RNC User Plane in WCDMA End-to-end Data Transmission Optimization Guide).
To judge whether there is packet loss, check whether the number of UL and DL
packets captured at the UE side is consistent with that at the Gi interface. If it is
inconsistent, there must be packet lost in the WCDMA system. Analyze user
tracing in SGSN, that in GGSN and captured packets at Gi interface to see in
which NE there is incoming data packets but no outgoing packets. Then the NE in
which the packet is lost can be located. Use the relevant NE equipment fault
location method to locate the fault. If permitted, capture packets at Gn interface
and compare the captured packets at Gn and Gi to judge whether the packets are
lost at GGSM.
For data transmission rate problem, if the UL and DL packet number in the UE
and that at the Gi is consistent, there is no packet loss in the WCDMA system, and
the problem may be caused by large system delay. Capture packets at the UE and
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Gi sides, and make comparison of the UL delay and DL delay. If the delay is large
but less than 1.5 s, and the service is based on TCP protocol, enlarge the TCP
window and run the service again. If the delay is large and less than 1.5 s, and the
service is VOD (RTSP/UDP/IP), response will not affect the DL packet
transmission but may affect the VOD play effect; if VOD service is discontinuous,
set the buffering time to be longer. If the delay is larger than 1.5 s which is
considered to be too large, the problem may exist at RAN or CN side. If there is
no problem at RAN side, there may be problem at CN side. Conduct mirror packet
capture at Gn and Gi interfaces of the GGSN to judge whether there is large delay
at the CN side. By experience, if there is no hardware bug, the delay at the CN
side should be small.
If the packet number in the UL and DL of UEs and that at Gi is consistent,
conduct data packet capture at the UE side to check whether the retransmitted data
at Gi interface has been received, and whether the received packets are correct
(through TCP validation). If the packets are wrong, which is serious, locate the
problem using the method described in the following sections, or ask help from
the R & D engineers.
The above procedures are targeting at the low rate problems; the procedures to locate
data transmission problem are similar.
1.2.2 Typical NE Locating Method
Using the above exclusive method, the NE can be located. As described above, PS
networking (not including access network) mainly involves the following equipment:
the SGSN, GGSN, switch, router, and firewall. Use the following method to locate the
NE.
1. SGSN user plane
Of the equipment listed above, the SGSN is the relatively complicated equipment with
many interfaces, and the data transmission function of the user plane has its own
features. Generally, lu interface between the RNC and SGSN is the ATM port, and the
interface between the Gn and Gp is IP Ethernet port (FE or GE). The data packets of
the UL user plane is transmitted as below: the RNC sends the packets of the user plane
to the forwarding engine of the specified UHPU via the ATM (the IPOA to the RNC
has been created in the forwarding engine). If the IP address of this forwarding engine
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Chapter 1 PS Service Data Transmission Analysis Method
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is the same with that of the destination of the data packet, the data packet will be
processed directly; otherwise, the forwarding engine will search for the route based on
the IP address of the data packet and send it to the destination forwarding engine (PDP
context is created on this forwarding engine). In
Figure 1-2, IPOA of the RNC is created in UHPU1, and users IP is created in UHPU2.
The SGSN conducts GTP processing, and then encapsulate the packets with the
destination IP address to be the IP address of Gn/Gp interface of the GGSN. Because
UHPU has routing function, and data packets can be directly sent to the Ethernet port
of the GFI board. Gn/Gp interface can also be the optical port, which is connected to
the router and then to other network equipment
EtherL
P
U
RNC
M
P
U
U
H
P
U
2
N
E
T
N
E
T
G
F
I
GGSN
Other SGSN
ATM
LPU-UHPU exchange data via 8850 NETGFI-UHPU exchange data via 8850NET
SGSN 8850 frame
U
H
P
U
1
Router
or
firewall
Router or
firewall
Figure 1-2 SGSN user plane
The procedures to handle the PS service problems relevant to the SGSN are:
Check that user tracing function is normal.
Confirm that PDP has been correctly created on the user plane.
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Check whether there is wrong statistics.
2. The packets are lost at GGSN.
If it is suspected that the packets are lost at GGSN, check it based on packet loss
statistics of the NP layer. The NP problem is caused by the product design; therefore
contact the product engineer to solve the problem.
3. Packet loss of data communication equipment.
Generally the current data communication equipment supports making packet loss
statistics. Execute commands to query the interface status, check the number of packets
received and sent to see whether there is any packet lost. It should be noted that the
packet loss of the data communication equipment does not indicate the equipment is
abnormal. For example, when filter ing rules are configured in the firewall,
unreasonable packets and attacking packets will be discarded. The configuration of the
equipment may lead to the loss of the correct packets. There are many data
communication equipment, please refer to their product command manual to see the
command to view the packet loss statistics.
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2 Data Analysis
Data analysis includes traffic statistics data analysis and DT/CQT data analysis.
Considering the practical demand of Network Planning and Optimization Dept., this
article mainly introduces the DT/CQT part. The data transmission problems of
WCDMA PS service falls into three categories in the aspect of phenomenon: access
failure (or dialing connection setup failure), successful access without the traffic flow,
and data transmission with low rate or great fluctuation. Different problems require
different analysis and handling processes.
General DT/CQT data analysis flow is shown as follows:
DT/CQT data analysis
Set up the PS service
successfully?
Data transmission
condition?
N
Y
No traffic flow on user plane
Low transmission rate and great fluctuation
Analyze the
problem of no
traffic flow on the
user plane.
Analyze poor data
transmission
performance.
Analyze data
transmission
interruption.
Data Transmission interruption
Analyze the
access failure.
Figure 2-1 Analysis flow of DT/CQT data
2.1 Basic Problem Analysis
2.1.1 Access Failure
There are two ways to launch the PS service. One is launching the PS service directly
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on the UE, and browsing the webpage and watching stream media through the UE
directly. The other is launching the service through personal computer in the method of
PC+UE, and using the UE as the Modem of the personal computer.
In the optimization test, the method of PC+UE is most commonly used. During the
DT/CQT test, the drive test tool software CNT runs on a personal computer, w hich is
usually a portable one. And this method is shortly called as CNT+UE. If the UE fails to
launch the PS service directly, the engineer can use the method of CNT+UE for further
verification to acquire more information. Therefore, the following problem analysis
focuses on CNT+UE.
2.1.1.1 UE directly launches the PS service
If the UE launches the PS service directly, the analysis flow of access failure is as
follows:
The analysis of access failure of the PS service launched by
the UE
UE fails to launch the PS servce directly?
N
Y
End
Analyze the access failure of the PS service launched in the
method of PC+UE
The PS service setup is a failure in the method of PC+UE?
Y
Check and modify the APN and the
webpage address setting of the UE.
N
Figure 2-2 Analysis flow of UEs failure of launching the PS service directly
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Chapter 2 Data Analysis
11
The process of launching the PS service directly on the UE and the process of
launching the PS service in the method of PC+UE are the same in the signaling flow,
but they have different APNs (name of the access point), and setting approaches of the
service visiting address. If the UE fails to launch the PS service directly, the engineer
can find the cause of the problem by taking the following steps.
1. Make verif ication in the method of PC+UE. If the PS service is normal, then the
system works normally. The engineer should check and modify the settings of
APN, service visiting address, Proxy and password of the UE.
2. If the access failure of PS service launched in the method of PC+UE happens, the
engineer should analyze and locate the problem according to section 2.1.1.2.
2.1.1.2 UE as the Modem of PC
If the UE is used as the Modem of the PC, the analysis flow of the access failure is
shown as follows:
The analysis of access failure
of the PS service set up in the
method of PC+UE
Port opening failure?
N
End
The signaling
process analysis
in the access
process
Access failure?
Y
YHandle the port
opening failure.
Y
Find the cause and solve the
problem?
Comparison and
analysis of the
operation type
N
N
Figure 2-3 Analysis flow of UEs failure of launching PS service
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1. Port opening failure
The analysis flow of port opening failure is shown as follows:
Handling port opening failure
Is the status of the port in Windows
Hardware Manager abnormal?
N
End
Maybe the port is not closed
normally. Restart the CNT
and the PC.
CNT abnormal termination happened
before?
Y
Y
Y
Maybe the UE software is
abnormal. Restart the UE.
N
Check and confirm CNT PORT
Configuration.
Insert and extract the UE.
N
Solve the problem?
Reinstall the UE driver.
Figure 2-4 Handling flow of port opening failure
The main causes of the port opening failure:
i Incorrect Port Configuration in the CNT
The engineer should check the Port Configuration in the CNT, and make sure the port
No. corresponds to the Com port and the Modem port in the Windows Hardware
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Chapter 2 Data Analysis
13
Manager.
ii Abnormal port status
Wrong driver installation and abnormal termination of the drive test tool during the
test may cause the status of the port mapped by the UE to become abnormal in the
Windows Hardware Manager. For example, the yellow exclamation mark appears.
Solution: Reinstall the driver, insert and extract the data cable or data card of the UE.
iii The port is not closed after abnormal termination of the software
During the test with the drive test tool such as the CNT, the software terminates
abnormally and may not close the corresponding port.
Solution: The engineer can try to restart the CNT software. If the problem still exists,
restart the personal computer.
iv Something wrong with the UE software
Try to solve the problem by restarting the computer.
v Incomplete installation of the UE driver
It is necessary to reinstall the driver, and this problem usually happens when the
personal computer is connected with the UE for the first time.
2. The port is opened successfully, but the access is still a failure.
In this condition, the failure is usually caused by the signaling f low, and the analysis
should focus on the signaling flow during the access process. The analysis flow is
shown as follows:
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The signaling flow analysis
during the access process
End
UE does not send Service
Request?
N
N
RRC connection failure? Y Analyze the RRC connection failure.
N
Analyze the problem that the UE does not
send the Service Request.Y
Are the authentification and
encryption processes
abnormal ?
YAnalyze the authentification and encryption
problems
Is the PDP activation refused?
N
YAnalyze the problem that PDP activation is
refused
Is the RB setup process
abnormal?Y Analyze the abnormal RB setup
Comparison and
analysis of the
operation type
N
Figure 2-5 Signaling analysis flow of access failure
Trace the NAS and RRC signaling in CNT or trace the single-user signaling in the
OMCR, and analyze the problems according to the standard data service signaling flow.
The problems may be:
i RRC connection setup failure
[Description]
Problems appear during the RRC connection setup process (From UE sending the RRC
Connection Request message to RNC receiving the RRC Connection Setup Complete
message).
[Analysis]
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Chapter 2 Data Analysis
15
If the engineer finds that the UE does not send the RRC Connection Request message
from the RRC Message traced by the CNT, the possible causes may be:
The Modem port is not selected during port configuration in the CNT.
The Test Controller in the CNT is not set, or is set incorrectly.
The UE port is abnormal. Details can be checked in Port Opening Failure in the
earlier part of this guide.
If the UE does not receive any responses, or receives the RRC Connection Reject
message after sending the RRC Connection Request message, the possible causes are:
Poor coverage
Admission refusal caused by uplink/downlink overload
Illegal parameter setting
For the illegal parameter setting, the main scenario is described as follows: the uplink
subscription request of the PS service is beyond the capability of the UE, which leads
to the direct refusal from the RNC. After the RAB setup failure caused by the incorrect
parameter setting which is beyond UE's capability, SGSN will negotiate a new RAB
assignment again to launch a new RAB assignment, until the UE has the capability to
support the assignment, and finally the RAB assignment is finished.
For the users, PDP activation can be successful, and the actual maximum rate is the
maximum rate the UE can support. However, if even the minimum guaranteed bit rate
required by the QoS setting in the UEs PDP activation request is beyond the UEs
capability, although the network has negotiated a lower rate to accept the PDP
activation request of the UE, the UE will send a request of deactivating PDP when it
finds out that the rate negotiated by the network in the PDP activation accept request is
lower than the minimum guaranteed bit rate, and finally, the PDP activation cannot be
completed.
ii UE does not send the Service Request message.
[Description]
There is no Service Request message in the NAS message.
[Analysis]
The possible causes may be:
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UE does not open the PS function
Some UEs can be set to support CS, PS, or CS+PS. If the UE is set to support CS, the
PS service cannot be set up. And then it is necessary to check the UE setting, and
modify it to PS or CS+PS.
UE does not finish the registration in PS domain.
Viewing from the signaling flow, the engineer finds that UE receives the Attach Reject
message from the network side after sending the Attach Reject message. The CN side
engineer should check whether the PS service is supported in USIM card subscription.
iii Problems in the authentication and encryption process
[Description]
The signaling flow between NAS signaling Authentication AND Ciphering REQ and
RRC signaling Security Mode Complete is abnormal.
[Analysis]
The CN side engineer should check whether the authentication switch in the PS domain
of the core network is opened, and whether the cryptographic algorithm and integrity
protection algorithm of CS domain, PS domain and RNC of the core network are
consistent.
iv PDP activation is refused.
[Description]
The UE sends the Activate PDP Context Request message, but receives the Activate
PDP Context Reject message.
The problems fall into two categories. One is incorrect setting of APN and rate
limitation at the UE side and the other is the core network problem.
APN setting problem at the UE side.
If the cause value of the Activate PDP Context Reject message is missing or unknown
APN, the cause is usually that the APN setting is not in accordance with that of the CN
side. The engineer can check the APN setting at the CNT+UE side, and compare it with
the HLR APN. The APN setting method of CNT and UE can be checked in CNT
Online Help. The CN side engineer should check the user's APN at the HLR.
Rate setting problem at the UE side
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Chapter 2 Data Analysis
17
If the cause value of the Activate PDP Context Reject message is Service option not
supported, the cause is that the rate required by UE is higher than the subscription rate.
The engineer can check the required rate setting at the CNT+UE side, and compare it
with the HLR subscription rate. The CN side engineer should be clear about the users
subscription rate in the HLR. The current APN and applied rate can be checked in the
Activate PDP Context Reject message.
Core network problem
If there are other cause values, and the APN and rate limitation setting at the UE side is
correct, the problem may lie in the core network, for example, some interfaces of the
core network are not through. The engineer can work with other engineers in the PS
domain of the core network to locate the problem. What is more, if the PS service is
debugged for the first time, the problem may be caused by the case that the
subscription APN in the HLR and that used in the GGSN are different. The engineer
can ask the personnel in charge of the PS domain of the core network for confirmation.
v RB setup failure
[Description]
After the Activate PDP Context Request message is sent, the RB setup message such as
the Radio Bearer Setup message is not received, but the release message is received
instead.
vi Others
Refer to the method described in Section 2.2.3, Comparison and Analys is of Operation
Type and compare the relative parts one by one to narrow the problem range.
2.1.2 No Traffic flow on the User Plane
The PS service is set up successfully on the signaling p lane, but there is no traffic flow
on the user plane. The problem analysis flow is shown as follows:
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18
Analysis of no traffic flow on
the user plane
End
DCH DCHE-DCH bearer judgment HSDPA
Find the cause of problem? Y
N
Analyze the problem
of no traffic flow on
the user plan at CN
side.
Y
Analyze the problem
of no traffic flow on
user plane on the E-
DCH at the RAN
side.
Comparison and
analysis of
operation type
Find the cause of problem?
N
Solve the problem?
Use corresponding
method to solve the
problem?
Analyze the problem
of no traffic flow on
user plane on the
DCH
at the RAN side.
N
Y
Figure 2-6 Analysis flow of no traffic flow on the user plane
2.1.2.1 Analysis of the Problem at the RAN Side
The successful setup of connection means there is traffic flow on the signaling plane.
But there is no traffic flow on the user plane, which may be caused by the TRB reset at
the RAN side. Especially for HSDPA, the service is borne on the HS-PDSCH, and the
signaling is borne on the associated DCH. When the HS-PDSCH does not have enough
power, there is traffic flow on the signaling plane, but no traffic flow on the user plane.
The following analysis is made from the two aspects of the PS service on the DCH and
the PS service on the E-DCH.
1. DCH Bearer
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Chapter 2 Data Analysis
19
Analysis of no traffic flow on user plane
on DCH at the RAN side.
Find the cause of problem?
N
End
OMCR tracing throughput
rate and bandwidth
Find the cause of problem?
N
Y
Analyze the problem of no
traffic flow on the user plane
at the CN side.
Y
Analyze the network coverage
Handle the problem or collect
information for feedback
Analyze whether there are
TBR reset at the association
log
Is the bandwidth normal?
Y
Figure 2-7 Analysis of no traffic flow on user plane at RAN side on DCH
i. Check the coverage
Trace the service cell pilot RSCP and Ec/Io in CNT+UE mode, and judge whether this
place is with poor coverage. If the RSCP is less than -100 dBm or the Ec/Io is less than
-18 dB, data service can hardly be finished.
Solution: If the RSCP is poor, improve the coverage angle to optimize it. If the
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20
RSCP is fine, but the Ec/Io is very poor, then the following checks are necessary:
Check the pilot pollution, and optimize the seriously polluted pilot.
Check the power configuration of the pilot channel, and the power is always
configured as 33 dBm.
Check and remove the outside interference.
ii. Check the call drop causes such as the TRB reset
Acquire the record of the associated log corresponding to the time point of the problem,
and check whether there is abnormal print near the time point of the problem to provide
the diagnostic message.
iii. Trace and measure the throughput rate and bandwidth of uplink/downlink.
Through monitoring the change of access layer rate and non-access layer rate of current
connected uplink/downlink data transmission, the engineer can analyze the dynamic
channel configuration function and the changing characteristic of the service source
rate conveniently. The engineer can locate the problem by checking which value is zero,
the uplink throughput rate or the downlink throughput rate. With the RNC DRBC
function open, the engineer should distinguish the bandwidth change caused by the
DRBC. If the engineer still cannot locate the problem, he needs to trace the user plane
and collect the number of the data packages received and sent by the RNC L2 and
GTPU to make sure the problem of no traffic flow on the user plane happens on the
uplink/downlink, at the CN side or the RAN side.
iv. Others
Check the problem at the CN side. Please refer to Section 2.2.3, Comparison and
Analys is of Operation Type for the operation method, and compare the relative parts
one by one to narrow the problem range. Then, make a feedback about the problem.
2. E-DCH bearer
The HSDPA feature of the cell is activated, and UE is able to support HSDPA. The rate
applied by the UE or the subscription rate is higher than the HSDPA threshold of
downlink BE service (for BE service), or the HSDPA threshold of downlink stream
service (for stream service). In this case, the PS service will be borne on the E-DCH,
and the engineer can check the following items.
i. The alarms and associated log in the RNC
-
Chapter 2 Data Analysis
21
Check the alarms and the associated log record to see whether there is anything
abnormal at the time point of the problem, and provide the diagnostic information.
ii. Deactivate the HSDPA feature, and set up the PS service on DCH.
With DEA CELLHSDPA, the engineer activates the HSDPA feature of the cell, and
builds dial-up connection to set up the PS service on DCH. If the data transmission of
the PS service on DCH fails, please refer to the earlier section for the handling method.
If the data transmission of PS service on DCH is normal, the problem locates at
HSDPA, and the engineer should continue with the following steps.
iii. Check the CQI, HS-SCCH scheduling success rate, SBLER and whether GBR is
configured.
Trace and record the UE reported CQI, HS-SCCH scheduling success rate and SBLER
reported by the UE in QXDM+UM mode.
a) CQI
The UE estimates and reports the UE reported CQI on the base of Ec/Nt of PCPICH. If
the UE reported CQI is zero, the NodeB will not send any data to the UE. If the
parameter configurations of pilot Ec/Io, CellMaxPower, PcpichPower, and MPO
constant are normal, but the CQI is poor, the engineer can try to change the personal
computer. PCs with different model have different noise floors, which will influence
the reported CQI at certain degree.
b) HS-SCCH scheduling success rate
The engineer can observe the HS-SCCH success rate at the WCDMA HSDPA
Decoding Statistics dialog box and the WCDMA HSDPA Link Statistics window of
QXDM.
-
UMTS PS Service Analysis
22
Figure 2-8 Example of dialog box showing the HSDPA parameter in QXDM
The HS-SCCH Success Rate (%) is the users HS-SCCH scheduling success rate which
is relative to the currently configured HS-SCCH channel number, accessed HSDPA
user number, and the scheduling algorithm parameter. If one HS-SCCH channel is
configured in the HSDPA cell, the RR scheduling algorithm is used, and all the
accessed UEs continue transferring data, then the HS-SCCH scheduling success rate of
every user is about the reciprocal of the HSDPA user number, which means all the
users share the resource of this HS-SCCH in time division.
If the users HS-SCCH Success Rate is about zero, then the use's data transmission rate
is about zero, which means there is no traffic flow on the user plane.
The possible reasons why the HS-SCCH Success Rate is about zero:
The MAX C/I scheduling algorithm is used, and there are more than one HSDPA
-
Chapter 2 Data Analysis
23
users accessed to this cell, with relatively low CQI.
The transmission power of the HS-SCCH is too low. Currently, the HS-SCCH
transmission power is configured as 2% of the total transmission power of the cell
in indoor scenario; and it is configured as 5% of the total transmission power of
the cell in outdoor scenario. If the transmission power of HS-SCCH is lower than
the standard mentioned above, there may be some troubles for UE to demodulate
the HS-SCCH.
There is no data to transfer on the application layer, and the engineer can confirm
this situation by checking the actual transmission data volume in RNC LMT by
choosing Connection Performance Measure -> Uplink Throughput rate and
bandwidth, Downlink Through rate and bandwidth.
The CQI reported by the UE is too low, which causes that the NodeB does not
schedule this user.
c) SBLER 100%
SBLER is the HS-DSCH block error rate. The above WCDMA HSDPA Decoding
Statistics dialog box shows the SBLER and retransmission conditions under different
TB, and in WCDMA HSDPA Link Statistics window, the HS-DSCH SBLER-Delta
and HS-DSCH SBLER-Average are shown, in which Delta is an instantaneous value,
and Average is an average value. The reason for the SBLER being 100% is that the
HS-PDSCH Ec/Nt is too low while the fundamental reason is that the HSDPA power is
not enough. The engineer can check the HSDPA power configuration which falls into
two categories: the static power configuration and the dynamic power configuration. If
this parameter is not less than the largest transmission power of the cell, this power
configuration is the dynamic configuration. Reversely, if this parameter is less than the
largest transmission power of the cell, this power configuration is the static
configuration. In the case of dynamic configuration, HS-PDSCH available power =
largest transmission power of the cell - power margin - R99 downlink load (including
common channel load) - HS-SCCH power; in the case of static configuration,
HS-PDSCH available = power of HS-PDSCH and HS-SCCH HS-SCCH power.
From the above two formulate, in the case of dynamic configuration, the high power
margin configuration, or R99 downlink overload or high HS-SCCH power
configuration may cause the problem that the HS-PDSCH available power becomes too
low. In the case of static configuration, the insufficient power of HS-PDSCH and
-
UMTS PS Service Analysis
24
HS-SCCH or excessive HS-SCCH power may cause the problem that the HS-PDSCH
available power becomes too low. The situation of SBLER being 100% caused by
insufficient power seldom happens, unless the CQI reported by the UE is too low. In
addition, the CQI calculated by the NodeB with insufficient power will be lower than
the normal value, and the TB scheduled by the NodeB will also be smaller than the
normal size. Therefore, the rate acquired by the UE will be reduced.
Solution: Correct the parameter configuration. If the R99 load is too high, the engineer
should consider carrier addition to solve the problem.
iv. Check the available bandwidth, the occupied bandwidth and the assigned
bandwidth of lub.
If the transmission data configuration is wrong, and the IMA group No.s of
AAL2PATH (for HSDPA) of the NodeB and the RNC are not corresponding to each
other, then the data transmission will not be through. If the product software problem
causes the problem that the HSDPA available bandwidth is insufficient, data
transmission will also be not through.
If the transmission configuration is in the ATM+IP mode, the HSDPA service is
transmitted in the IP mode, and the signaling is transmitted in the ATM mode, then the
FE interruption will cause the problem that the signaling can be transmitted, but there
is no traffic flow on the user plane.
2.1.2.2 Analysis of the Problem at the CN side
The problem at the CN side may be caused by the service server with problem, the
incorrect user name and password and so on.
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Chapter 2 Data Analysis
25
Analysis of the problem of no traffic flow
on user plane at the CN side
Is it normal to use the service
through the LAN/other radio
networks?
N
End
Check the user name and the
password. Y
The CN side is normal.
Check whether the server
and service software operate
normally.
Figure 2-9 Analysis of the problem of no traffic flow on user plane at the CN side
The engineer can make sure that the service software server and the service software
runs normally through other access networks (or LAN).
1. LAN
Through the personal computer on the LAN, the engineer can perform the FTP or
HTTP service to make sure that the services are normal and verify the accessible user
name and password.
-
UMTS PS Service Analysis
26
2. Other radio access networks in the same core network
Establish the PS connection on 3G access networks in the same core network or on the
GPRS, and then check whether the service is normal. If the engineer finds the service
server works normally after finishing the above step, he should analyze the problem at
the RAN side. If the engineer finds that the service server works abnormally, the
problem must lie in the CN.
i. HLR
One SIM card can be configured with multi APNs, and each APN corresponds to a
highest rate. When there is no maximum rate limit at the UE side, the RAB assignment
request message delivered by the core network carries the subscription rate of the user.
If there is no limit on the power, code resource and other resources at the RNC side, the
assigned rate will be sent to the UE through the Activate PDP content Accept message
in the NAS signaling, and the rate in the PDP activation acceptance can be viewed in
the QXDM or other drive test tools.
ii. GGSN
To modify the users QOS parameter on GGSN, the engineer should set the downlink
bit rate and guaranteed rate which are 384 kpbs by default. Set the maximum downlink
rate as 2048 kpbs, so that the CN allows the HSDPA downlink maximum rate to be 2
Mpbs.
iii. SGSN
The SGSN uses SET 3GSM to modify the users downlink maximum rate and
guaranteed rate to 2 M.
iv. Summary
The checking result shows that the cells have been established. Therefore problems at
the RAN side can be excluded. Then the engineer should check the HLR subscription
rate and the users QoS parameter of the SGSN and the GGSN at the CN side.
2.2 Problems of Data Transmission Performance
From the aspect of throughput rate measurement, the poor data transmission
performance is represented as unstable and low rate, and great fluctuation. From the
aspect of service quality, poor data transmission performance is represented as poor
-
Chapter 2 Data Analysis
27
stream media graphic quality, the need to buffer stream media and slow webpage
response. The PS data transmission path is shown in Appendix 8.1, and the PS data
mainly passes the internet service server, the GGSN, the SGSN, the RNC, the NodeB,
and finally arrives at the UE. During the transmission, the data passes five interfaces:
Gi, Gn, IuPS, Iub, and Uu. In this process, the internet server communicates with the
GGSN by the IP protocol, and there are one or more route equipment and firewall
between them. The PS service takes the AM mode of the RLC, and it is equipped with
the retransmission function. For the FTP and HTTP service, the TCP protocol, which
also has the function of retransmission, is used for communication. The parameters of
the two protocols (RLC/TCP) have great influence on the rate. If the parameters are
improperly configured, or packet error and packet loss happen during the transmission,
the data rate may be reduced. When observing the service quality, the engineer always
uses the application program on the computer with the UE as the MODEM to judge the
quality, then the performance of the computer and the server is involved. Therefore,
there are many factors affecting the PS data transmission performance, and these
factors fall in the categories of the access network problem, the core network
equipment problem, and the application and the service software problem. In this guide,
the application and service software problem and the core network equipment problem
are generalized as the problem at the CN side; and the access network problem is
referred as the problem at the RAN side.
The analysis flow of poor data transmission performance is shown as follows:
-
UMTS PS Service Analysis
28
Analysis of the problem of
poor data transmission
performance
End
Find the cause of the problem?
Judge the RAN/CN problem
Analyze the problem
of poor data
transmission
performance at the
CN side.
Comparison and
analysis of the
operation type
Find the cause of the problem?
Solve the problem?
Check the alarm
N
Analyze the problem
of poor data
transmission
performance at the
RAN side.
RAN Problem CN Problem
Handle the problem with
effective measure.
Y
Y
Y
N
Figure 2-10 Analysis flow of data transmission performance problem
2.2.1 Checking the Alarms
After the problems appear, the engineer should check whether there is alarm appearing.
The alarms of the NodeB and the RNC at the RAN side, and the alarms of SGSN,
GGSN, LANSWITCH, ROUTER, FIREWALL and other NEs at the CN side should be
checked. The alarms of the clock problem, the transmission errors, the instantaneous
interruption of transmission and other abnormal conditions of the equipment may affect
the data transmission. If the engineer cannot locate the problem by alarms of NEs, he
-
Chapter 2 Data Analysis
29
should make comparison and analysis of the operation type, and try to screen out the
affecting factors and narrow the range of the problem. If the cause of the PS data
transmission problem can be determined to be at the RAN side, the engineer should
analyze the problem at the RAN side; If the service is established on the DCH, the
engineer should follow the procedures in section 2.2.4 R99 Problem; if the service is
HSDPA, the engineer should follow the procedures in section 2.2.5 HSDPA Analys is;
if the service is HSUPA, the engineer should follow the procedures in section. If the
cause of problem can be determined to be at the CN side, the engineer should analyze
the data transmission problem at the CN side. If the cause the problem cannot be fixed,
the engineer should analyze from both the RAN side and the CN side.
2.2.2 Factors Affecting the Data Transmission at the lub Interface
The Iub interface transmission error, delay jitter, and lub bandwidth problem will affect
the data transmission. The analysis flow is shown as follows:
Analysis of the factors
affecting data transmission at
the lub interface
Is there any alarm for abnormal
transmission/clock problem? Y Handle the problem.
End
N
Iub bandwidth congestion? YIncrease the
transmission resource.
N
Check the alarm.
Check the lub
bandwidth.
Figure 2-11 Analysis of the factors affecting the data transmission at the lub interface
-
UMTS PS Service Analysis
30
1. Transmission error and delay jitter
The engineer can check whether the problem exists by checking the transmission alarm
and the clock alarm.
2. Iub bandwidth problem
The methods of checking whether lub congestion exists are shown as follows:
RNC probe and NodeB PM checking
Lub bandwidth performance checking
The abnormal record in the association log checking
2.2.3 Comparison and Analysis of Operation Type
Comparison and analysis of the operation type is to find out the NE on which the
problem happens, and tell where the cause of the problem is: the core network or
service software or the access network. The comparison includes the following
operations:
Changing the USIM card, the cell phone/data card and the PC;
Changing the webpage, gateway and the service mode;
Changing the networks in the same server, for example, 2G or other 3G networks
Table 2-1 Comparison and Conclusion
No. Operation Result Conclusion
1 Changing the USIM card
The data transmission
returns to normal.
The problem may relate to
the USIM card
subscription.
The data transmission
problem still exists.
The cause cannot be
located, and the engineer
should continue the
troubleshooting.
2 Changing the cell phone/data card
The data transmission
returns to normal.
This problem may relate
to UE, for example, the
compatibility or the UE
performance problem.
The data transmission The cause cannot be
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Chapter 2 Data Analysis
31
No. Operation Result Conclusion
problem still exists. located, and the engineer
should continue the
troubleshooting.
3 Changing the personal computer
The data transmission
returns to normal.
This problem may relate
to the drive program
installation, APN setting
in the personal computer,
rate limit setting and the
firewall.
The data transmission
problem still exists.
The cause cannot be
located, and the engineer
should continue the
troubleshooting.
4
Changing the service in the same
server ( making sure that the
server is in the normal working
status, and trying the PING and
stream media service)
The data transmission
returns to normal.
The cause is the problem
at the CN side, and may
relate to the service
software.
The data transmission
problem still exists.
The cause cannot be
located, and the engineer
should continue the
troubleshooting.
5 Changing the website (making the
download from other websites)
The data transmission
returns to normal.
The cause is the problem
at the CN side, and may
relate to the server
performance, TCP/IP
parameter or the service
software.
The data transmission
problem still exists.
The cause cannot be
located, and the engineer
should continue the
troubleshooting.
6
Changing other access networks in
the same server, such as the GPRS
network.
The data transmission
returns to normal.
The cause is the problem
at the RAN side.
The data transmission
problem still exists.
The cause cannot be
located.
7 Testing other NodeBs The data transmission
returns to normal.
This problem is caused by
the NodeB problem or the
improper configuration of
RNC parameters related
with the NodeB.
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UMTS PS Service Analysis
32
No. Operation Result Conclusion
The data transmission
problem still exists.
The cause cannot be
located.
What is more, for further troubleshooting, the engineer can send the data from the
upper level equipment to the UE for comparison.
Table 2-2 Packet Delivery Check and Conclusion
No. Operation Result Conclusion
1 Delivering packets actively from
PDN to UE
The downloading returns
to normal
The cause is not CN and
RNC problem
The downloading problem
still exists
The cause is CN or RNC
problem.
2
Delivering packets actively from
RNC to UE.
The downloading returns
to normal
The cause is the problem
at the RNC side.
The downloading problem
still exists
The cause is the problem
at the RAN side.
3 Delivering packets actively from
NodeB to UE
The downloading returns
to normal
The cause is the problem
at the IUB interface.
If the engineer still cannot find out where the problem lies after making the comparison
and analysis according to the above operation step by step, he should analyze the
problems step by step in the sequence of the RAN side and the CN side.
2.2.4 R99 Problem
The analysis flow of the poor data transmission performance on DCH at RAN side:
-
Chapter 2 Data Analysis
33
End
Analysis of the problem of
poor data transmission
performance at the RAN
side.
Find the cause of the problem?
N
N
Is there any alarm at NE? Y Handle the alarm.
Y Handle the problem.
Analyze the
factors affecting
the data
transmission at
the Uu interface.
Analyze the
factors affecting
the data
transmission at
the lub interface
Find the cause of the problem?
N
Y Handle the problem.
Is the ratio of APP/RLC
throughput too low?Y
Check the TCP receiving
window and MTU setting.
N
Figure 2-12 Analysis flow of the problem of poor data transmission performance on the DCH at the
RAN side
2.2.4.1 Factors Affecting the Data Transmission at the Uu Interface (DCH)
If the PS service is on the DCH, the factors affecting the data transmission at the Uu
interface mainly include the allocated channel bandwidth, the state migration
occurrence and the error condition at Uu interface. The analysis flow is shown as
follows:
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UMTS PS Service Analysis
34
Analysis of the factors
affecting the data
transmission at the Uu
interface
Analyze the
bandwidth of the
DCH.
Analyze the error
at the Uu
interface.
Find the cause of the problem? Y Handle the problem.
End
N
Find the cause of the problem? Y Handle the problem.
N
Figure 2-13 Analysis of the factors affecting the data transmission at the Uu interface
1. DCH Bandwidth
When the PS service is on the DCH, RNC allocates certain channel bandwidth for
every accessed UE. The size of the bandwidth is decided by the spreading factor and
the coding method of the code resource. Open the uplink/downlink throughput and
bandwidth real-time measurement provided by the OMCR to see the uplink/downlink
bandwidth allocation and the throughput. Bandwidth shows the channel bandwidth of
UE allocated by the RAN, and DlThroughput is the actual downlink data transmission
rate. If bandwidth is the same as the rate when UE applies the PS service, or as the UE
subscription rate, or as the maximum rate in the case of DCH bearer, such as 384 k,
then the bandwidth allocation is normal, that is to say the allocation of code resource,
power resource and lub bandwidth is normal.
If the above measurement shows that the UEs allocated bandwidth is lower than that
-
Chapter 2 Data Analysis
35
in expectation, there are two possible causes. One is that the channel with higher rate
cannot be allocated to the UE because of the congestion and other abnormal reasons,
which is an abnormal condition. The other is the DRBC algorithm of RNC. If the
parameter of the DRBC algorithm is reasonable, this rate decrease is normal. For the
current network, it is necessary to open the DRBC algorithm, so that the system can
reduce the allocated bandwidth to save the resource when the transmitted data is
reduced or the transmission is suspended temporarily. However, sometimes the
algorithm may be set improperly. According to the condition of the traffic volume,
coverage and soft handover, the rate can be adjusted through the DRBC algorithm.
Based on the on-site configured parameter, taking the algorithm into account, the
engineer should check whether the current bandwidth allocation and adjustment is
reasonable, whether there is anything abnormal and whether it is necessary to adjust
the parameter to solve the problem. For the low bandwidth caused by congestion and
other abnormal conditions, the engineer can make single-user tracing, check the
downlink load and code resource allocation and the size of the lub available bandwidth,
and acquire the corresponding association log to check the abnormal printing
information, then the clue of the problem can be found.
2. Error at the Uu Interface
The uplink/downlink error at the Uu interface directly affects PS throughput. If the
average values of the measured UL BLER and DL BLER during a certain period of
time are near or better than the BLER Target, the error condition at the Uu interface is
normal. Otherwise, it is necessary to analyze the factors causing the error at the Uu
interface.
DL BLER measurement: Use CNT+UE to collect the drive test file, and import CNA
analys is.
UL BLER measurement: click OMCR Connection Performance Measure -> Uplink
Transmission Channel Block Error Rate. Make comparison between the block error
rate and the CNT drive test file.
Power control and coverage are the main factors affecting the uplink/downlink BLER.
i. External loop power control switch
The engineer should make sure that the RNC external loop power control switch is
open.
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UMTS PS Service Analysis
36
ii. Coverage
The engineer should make sure that the uplink/downlink power is limited in the area
with poor UL BLER and DL BLER.
iii. UE performance
The engineer can try to change the UE, or compare the current UE and the UE of other
types.
3. In-sequence delivery
Setting the In-Sequence Delivery to TRUE or FALSE will affect the rate and
fluctuation of uplink data transmission. If the In-Sequence Delivery is set to TRUE,
RLC will keep the transfer order of the high-level PDUs. If it is set to FAUSE, RLC
entity which receives the data will allow the SDUs to be transferred to the high-level in
the order different from that of the sender, and then the uplink data transmission rate
will be low, with great fluctuation. It is suggested to set the In-Sequence Delivery to
True, and the setting can be modified in HLR of CN.
2.2.4.2 Comparison of the Throughputs on APP Level and RLC level
The engineer can acquire the throughputs on APP level and RCL level through
DT/CQT test.
If Throughput on APP level/ Throughput on RLC level is lower than the normal range
of theoretical analys is, it means the TCP/IP retransmission costs too much overheads.
TCP receiving window and MTU setting can be checked and modified.
2.2.4.3 Data Transmission Interruption Analysis
1. Phenomenon: Data transmission is interrupted for a period of time during the
transmission process.
2. Possible Reasons:
i. Call drop during the data transmission;
ii. The data transmission is interrupted after the handover from 3G to 2G;
iii. The state migration from CELL_DCH to CELL_FAC and CELL_PCH happens
during the data transmission. When the data transmission is recovered, the
systems cannot migrate back to CELL_DCH status, because the resource is not
enough. And the data transmission will be affected.
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Chapter 2 Data Analysis
37
iv. Other abnormal conditions, such as transmission interruption
3. Analys is: The engineer analyzes this problem from the aspects of alarms,
signaling flow and association log.
Analysis of the data
transmission interruption
Is there any alarm? Y Handle the problem.
End
N
Is there any state migration?
N
Y
Analyze the problem that
the bandwidth can not
recover after the state
migration.
N
Is there any call drop? Y Analyze the call drop.
Is the data transmission
interrupted after the 3G/2G
handover?
N
YAnalyze the 3G/2G
handover
Figure 2-14 Analysis flow of data transmission interruption on DCH
i. Alarms
The engineer checks the alarms of CN and RAN NE, understands the abnormal
condition of the current system, and guide the problem analysis and troubleshooting.
The engineer can find out the problems such as the transmission interruption, the cell
clock asynchronizaiton and the NE congestion through the alarms.
ii. Signaling Flow
The data transmission problem location mainly depends on the signaling specific
-
UMTS PS Service Analysis
38
analys is, for example, judging whether there is call drop, handover from 3G to 2G, and
channel state migration. There are two ways to collect the signaling: one is to use
CNT+UE to collect the signaling sent and received at the UE side, the other way is to
use the OMCR single-user tracing to collect the signaling sent and received at the RNC
side. Through the comparison of the signaling collected by the two ways, the engineer
can check whether there is message loss caused by the air interface with poor quality.
What is more, the engineer can take the association log into account to locate the
problem.
Call drop
Channel state migration
After the channel status is migrated to the common channel, the channel cannot
migrate back to the CELL_DCH status. The engineer can check the abnormal printing
of the association log to check whether the problem is caused by the downlink overload
or the lub bandwidth congestion. To solve the problem, the engineer can add the
carriers or the transmission resources.
Handover between 3G and 2G
The data transmission failure caused by the handover from 3G to 2G relates to the
coordination of the two networks. If the 2G network is HWs network, the problem
location is even harder. Firstly, the engineer checks whether the PS service can be
normally set up on the 2G system. If the data transmission is normal when the 2G
network is accessed, and it becomes abnormal after the handover, then the engineer
should check the UE side, and the signaling flow at the 3G and 2G equipment. The
cause of the problem may be the unsuccessful update of the routing area caused by the
inconsistent cryptographic algorithm configuration of subscription and Authentication.
2.2.5 HSDPA Analysis
HSDPA schedules power and code resources among multiple users in code-division or
time-divis ion mode. Under the single-user condition (that is when there is only one
HSDPA user in the cell), the factors that affect data transmission rate are available
power for HSDPA, the number of HS-PDSCH codes (only one HS-SCCH channel is
needed under the single-user condition), the UE category (the maximum number of
codes supported by the UE and the availability of 16QAM support function), radio
signals at the location of the UE, the UEs subscription rate, Iub bandwidth, and the
-
Chapter 2 Data Analysis
39
maximum rate supported by the RNC, NodeB, GGSN, and SGSN. Under the
multi-user condition, apart from the above factors, the algorithm used in the NodeB,
the number of HS-SCCHs configured for the cell will also affect the data transmission
rate.
2.2.5.1 HSDPA Working Process
1. The UE reports CQI on the HS-DPCCH, and the NodeB acquires the channel
quality of the location of the UE.
2. The scheduling module in Node B evaluates different UEs on the channel
condition, the data volume in each UEs buffer area and the latest service duration
to determine the HS-DSCH parameters.
3. The NodeB sends the HS-DSCH parameters on the HS-SCCH, and then sends the
parameters on the HS-DSCH after 2 slots.
4. The UE monitors the HS-SCCH to see whether there is any information for itself.
If there is, then the UE starts receiving data from the HS-DSCH and then cache
the data.
5. According to information on the HS-SCCH, the UE can judge whether to integrate
the data received from the HS-DSCH with that in the soft buffer area.
6. The UE demodulates the data received from the HS-DSCH, and sends the
ACK/NACK in response to the uplink HS-DPCCH according to the CRC results.
7. If the NodeB receives NACK, it will resend the data until it receives ACK from
the UE or until the number of resending times reaches the maximum value.
2.2.5.2 Problem Analysis Process
To test the HSDPA performance of the system, we usually download big files in
5-thread mode from the FTP server and observe the downlink throughput rate. All the
abnormities described later in this article take place when the data at the service
resource is sufficient.
-
UMTS PS Service Analysis
40
End
Analyzing poor data
transmission problem
at RAN side
Low Scheduled Rate
N
N
N
Is there any NE alarm? Y Handle alarms
YHandle the
problem
Low MAC Layer Rate
N
Y
Handle the
problem of high
SBLER
The throughput rate of
APP/RLC is too small?Y
Check the TCP
receiving window
and MTU setting.
N
Services based on
HSDPA?Y
Handle the
problem
Low Served Rate
N
Y
Handle the
problem of low
HS-SCCH
success rate.
Low RLC Layer Rate YHandle the
problem
N
Figure 2-15 Analysis process of poor data transmission performance on E-DCH
2.2.5.3 Whether Services are borne on HSDPA
Judge whether the services are based on HSDPA from the following aspects:
1. Whether the cell supports HSDPA: Check whether the HSDPA cell at the RNC
side has been activated, and whether the attribute of the local cell at the Node B
side has been configured to support HSDPA.
-
Chapter 2 Data Analysis
41
2. HSDPA services access failure will also cause the RNC to reconfigure HSDPA
services to 384 kbps as R99 services. Check whether the following configurations
are reasonable: the uplink and downlink load of R99 services, downlink code
resource, Iub transmission resource, the number of HSDPA services users, the
total rate threshold in the HSDPA cell, the guaranteed rate threshold and the
guaranteed power threshold of stream services.
3. The HSDPA threshold of downlink BE services is too high. The HSDPA threshold
of downlink BE services determines the rate decision threshold of the PS domain
Background/Interactive services on the HS-DSCH. Only when the maximum
downlink rate of the PS domain Background/Interactive services is not less than
this threshold, can the services be borne on the HS-DSCH; otherwise, they will be
borne on the DCH.
2.2.5.4 Locating Scheduled Rate Problem
During the NodeB scheduling process, TB size is decided by CQI, code, and power.
And TB size/2 ms are the scheduled rate. In the normal condition, scheduled rate and
the UE reported CQI are in a mapping relationship (which depends on the NodeB CQI
mapping table in practical use). Strictly speaking, because the NodeB will filter and
correct the UE reported CQI, in fact the scheduled rate may be in a mapping
relationship with the NodeB scheduled CQI, rather than with the UE reported CQI.
Therefore, the following table shows the corresponding relation between CQI and the
reference TB size according to the protocol 25.306, and the relation between CQI and
the scheduled rate can be worked out.
Table 2-3 CQI Mapping Table When UE Level is 11-12
CQI value Transport Block Size Number of
HS-PDSCH Modulation
Reference power
adjustment
0 N/A Out of range
1 137 1 QPSK 0
2 173 1 QPSK 0
3 233 1 QPSK 0
4 317 1 QPSK 0
5 377 1 QPSK 0
6 461 1 QPSK 0
7 650 2 QPSK 0
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UMTS PS Service Analysis
42
8 792 2 QPSK 0
9 931 2 QPSK 0
10 1262 3 QPSK 0
11 1483 3 QPSK 0
12 1742 3 QPSK 0
13 2279 4 QPSK 0
14 2583 4 QPSK 0
15 3319 5 QPSK 0
16 3319 5 QPSK -1
17 3319 5 QPSK -2
18 3319 5 QPSK -3
19 3319 5 QPSK -4
20 3319 5 QPSK -5
21 3319 5 QPSK -6
22 3319 5 QPSK -7
23 3319 5 QPSK -8
24 3319 5 QPSK -9
25 3319 5 QPSK -10
26 3319 5 QPSK -11
27 3319 5 QPSK -12
28 3319 5 QPSK -13
29 3319 5 QPSK -14
30 3319 5 QPSK -15
Table 2-4 CQI Mapping Table When UE Level is 1-6
CQI
value
Transport
Block Size
Number of
HS-PDSCH Modulation
Reference power
adjustment
0 N/A Out of range
1 137 1 QPSK 0
2 173 1 QPSK 0
3 233 1 QPSK 0
4 317 1 QPSK 0
5 377 1 QPSK 0
6 461 1 QPSK 0
7 650 2 QPSK 0
8 792 2 QPSK 0
9 931 2 QPSK 0
10 1262 3 QPSK 0
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Chapter 2 Data Analysis
43
CQI
value
Transport
Block Size
Number of
HS-PDSCH Modulation
Reference power
adjustment
11 1483 3 QPSK 0
12 1742 3 QPSK 0
13 2279 4 QPSK 0
14 2583 4 QPSK 0
15 3319 5 QPSK 0
16 3565 5 16-QAM 0
17 4189 5 16-QAM 0
18 4664 5 16-QAM 0
19 5287 5 16-QAM 0
20 5887 5 16-QAM 0
21 6554 5 16-QAM 0
22 7168 5 16-QAM 0
23 7168 5 16-QAM -1
24 7168 5 16-QAM -2
25 7168 5 16-QAM -3
26 7168 5 16-QAM -4
27 7168 5 16-QAM -5
28 7168 5 16-QAM -6
29 7168 5 16-QAM -7
30 7168 5 16-QAM -8
The factors that affect the scheduled rate are CQI, HSPDA cell available power, and
HSDPA cell available codes. The analysis can be made from the following
perspectives:
1. CQI
i. Problem of low CQI
If the UE downlink rate is low, check whether the UE reported CQI is too low and at
the same time check the RSCP and Ec/lo of the PCPICH in the current cell. The
problem may be caused by:
The coverage is poor and the UE reported CQI is low.
Interference is relatively serious, the pilot is polluted, and the UE reported CQI is
relatively low.
If the HSDPA user changes cells frequently, he/she will be forbidden changing
cells as a punishment. Therefore the UE reported CQI will be low.
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44
Poor receiving performance of some UE built- in antennas or UE individuality will
also cause low UE reported CQI and therefore affect rate.
ii. Solutions :
For the poor coverage problem, optimize RF or add sites to improve the UE
reported CQI.
For the serious interference problem, optimize RF to adjust the antenna directional
angle and the down tilt angle to provide a dominant serving cell.
For the problem of the frequent change of HSDPA cells, optimize RF to adjust the
antenna directional angle and down tilt angle or add sites to avoid frequent
handover. In addition, in our system, there is a timer (T1d), which defines the
punishment time between cell changes. This time is 4 seconds by default, but in
fact, this time is too long so that it affects the HSDPA throughput rate. Therefore,
the plan is to set it to 0 second or 2 second.
For the UE problem, it is suggested to exclude other problems before changing it.
2. HSDPA cell available power
If the available power for the HSDPA cell is too low, it will affect the TB size during
the NodeB scheduling process. HSDPA power can be configured in dynamic mode or
in static mode.
If HSDPA power is dynamic configuration, HSDPA available power = total power of
the cell x (1- power margin) - the power of R99 service channel and common channel.
Static configuration of HSDPA power means HSDPA available power is the initially
configured HSDPA power. However, the maximum power in practical use can only be
the result of the formula: total cell power x (1- power margin) - power of the common
channel. Please note that even in the static power configuration mode. R99 services
will take the power of HSDPA services because of the power control. Therefore, the
HSDPA power in practical use may not be the configured power.
The available power of HSDPA cells can be affected by the following factors:
i. HS-PDSCH MPO constant
The HS-PDSCH MPO constant can be modified in the RNC OMC. Under the
condition of HSDPA, the UE reports CQI, and according to the reported CQI, the
NodeB can judge the quality of the current radio link and adjust the TB size and the
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Chapter 2 Data Analysis
45
power. When the UE reported CQI is less than 5, the NodeB will not send data to this
UE. And the MPO constant can adjust the UE reported CQI, which can be calculated
based on the pilot Ec/Nt. The formula is as follows:
UE reported CQI = (Ec/Nt)CPICH + 10*lg(16)+MPO+4.5
In the formula, 4.5 is a fixed constant which is obtained from simulation. 10*lg(16) is
the spreading gain used to calculate the HS-PDSCH (SF=16).
ii. HS-SCCH power
The HS-SCCH power can be configured in static mode or dynamic mode. In static
mode, the HS-SCCH power is configured to a percentage of the maximum emission
power of the cell. This percentage is 2.5% for now. In dynamic mode, the power of
the HS-SCCH can be adjusted dynamically.
3. HSDPA cell available codes
Configuration of SF for the downlink physical channel of HSDPA cells: While
configuring SF for the HSDPA cell, in addition to the common channels as for R99
cells, SF codes should also be reserved for the HS-SCCH (static configuration only)
and the HS-PDSCH (when code resource is allocated in static mode). For the
HS-SCCH, SF is fixed to 128, and for the HS-PDSCH, SF is fixed to 16. In this
condition, R99 users cannot take the code resource configured for HSDPA.
i. When the code resource is allocated in dynamic mode, usually the OMC will
assign the initial number of HS-DSCHs, the maximum number of HS-DSCHs and
the minimum number of HS-DSCHs. The number of HS-DSCHs occupied by
users should be between the maximum one and the minimum one. If more R99 CS
users need to access the network, they may take the HSDPA code resource.
ii. HSDPA accompanies the DCH code resource allocation. When a user applies the
high speed PS services, the system will bear the services on HSDPA. This user
occupies the HS-SCCH and the HS-PDSCH, and meanwhile when the services
are being established, the user will be assigned with an associated DCH (A-DPCH)
to transmit signaling at 3.4 kbps. This channel is a dedicated downlink channel
with SF256.
iii. If the codes allocated to HSDPA users are too few, the TB size scheduled by the
NodeB will also be affected.
4. HSDPA UE capacity
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UMTS PS Service Analysis
46
i. Protocol 25.306 specifies 12 categories of UE. In one TTI, different UE categories
obtain different maximum TB sizes. Therefore the maximum scheduled rate
obtained by the UE is different.
ii. In the message RRC Connection Setup Complete the UE will report its capacity.
The IE (information element) of HSDSCH physical layer category reflects the
UEs ultimate capacity.
5. The data volume that can be scheduled by the UE is smaller than the largest TB.
The TB size scheduled by the NodeB depends not only on the UE available power and
codes, but also on the data volume that can be sent by the UE. If the data volume sent
by the UE is smaller than the largest TB, then the physical layer rate will be lower than
the expected value. This problem usually occurs when there is still data in the NodeB
buffer area, but the data volume is smaller than the largest TB that can be scheduled.
2.2.5.5 Locating Served Rate Problem
According to the formula: Served Rate = Scheduled Rate * HS-SCCH Success Rate,
when the scheduled rate is normal, low served rate is due to low HS-SCCH success
rate. Under the condition of single user, if the power and traffic volume of the
HS-SCCH do not have limit, the success rate of the HS-SCCH should be 100%. Users
HS-SCCH success rate is related to the HS-SCCH power, the number of the HS-SCCH
channels, the number of users, scheduling algorithm, and the transmittable traffic
volume.
1. HS-SCCH power ratio
The HS-SCCH is a downlink common channel, which can be shared by all the users.
The UE keeps monitoring the UE ID on the HS-SCCH, and judges whether TTI directs
to itself. If it is, the UE will demodulate the HS-PDSCH data. Therefore, the HS-SCCH
must be correctly demodulated before data transmission.
2. Number of HSDPA users and number of HS-SCCHs
The success rate of the HS-SCCH is also related to the number of users. If there is only
one HSDPA user, no limit on traffic volume and the HS-SCCH power is enough, then
the HS-SCCH success rate of this user is nearly 100%. If there are multiple HSDPA
users in the cell, the HS-SCCH success rate of each user depends on the scheduling
algorithm and the number of HS-SCCHs. Usually, according to the HS-PDSCH
available power, code resource and the traffic volume at the traffic resource. it is
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Chapter 2 Data Analysis
47
suggested to configure the HS-SCCH for UE level 12 in the following ways:
i. Configure 5 codes for the HS-PDS and two HS-SCCHs
ii. Configure 10 codes for the HS-PDSCH and three HS-SCCHs
iii. Configure 14 codes for the HS-PDSCH and four HS-SCCHs
3. Scheduling algorithm
Under the multi-user condition, the probability of each user being scheduled varies
from different algorithms. For instance, if the MaxC/I scheduling algorithm is adopted,
the user at distance will have less probability to be scheduled because its CQI is
relatively low; the probability can be 0 in this case. Scheduling algorithm is the
function of the HSDPAs newly added function entity MAC-hs, which takes four
factors into account: CQI, length of the waiting time, priority in the queue, and length
of the queue. CQI indicates the signal quality of the UE location; length of the waiting
time (Wait_Inter_TTI) indicates the interval during which the UE waits for services.
The typical scheduling algorithms are listed below:
i. MaxC/I (taking only the CQI value into account)
ii. RR (taking only the length of waiting time into account)
iii. PF (Proportional Fair, taking all the factors above into account)
In terms of fairness, RR algorithm is the fairest way, and after it comes the RF
algorithm. Max_C/I are the most unfair way. In terms of the cell throughput rate,
MAX_C/I are the best algorithm, and PF comes after it. The worst one in this case is
the RR algorithm. In terms of commercial network, for the balance of fairness and
throughput rate, the RF algorithm is recommended. Because this algorithm takes into
account the users throughput rate history and the condition of channels. Operators can
choose whatever algorithm according to the actual situation.
4. Traffic volume
After parameters configuration check, if no problem is detected, the UE reported CQI
is relatively high, and neither power nor code resource nor transmission resource is the
bottleneck, but the users rate is still unstable, then through the UEs HSDPA in the
PMS you can measure whether the data coming from Iub is sufficient to be scheduled.
The cause of insufficient data may be that the rate at the data resource is not stable, or
the download mode is single-line mode and meanwhile the TCP window configuration
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UMTS PS Service Analysis
48
is small.
5. Speed limit at UE side
The requested service type and highest downlink/uplink rate can be sent to the UE by
the command of AT, and the UE will send the information to the CN in the follow -up
signaling of Active PDP context request. When the subscription rate is not lower than
the maximum rate of this request, the CN will send RAB Assignment request at the
highest rate of the request sent in AT command. If there is no resource limit at the RNC
side, the service will be supplied at this rate. If the highest downlink rate in the RAB
assignment request is much lower than the scheduled rate, and the traffic volume in the
buffer area is insufficient to be scheduled by the NodeB, then the success rate of the
HS-SCCH will be low.
i. Setting rate by the command of AT
Click My computer -> Property (Management) -> Hardware -> Device manager
-> Demodulator -> Attribute -> Advanced, and enter AT command in the initial
command line. Apart from rate limit, usually it is also required to set APN in the AT
command. To set APN to cement, the rate limit to uplink 64 kbps, downlink 384 kbps,
the AT command should be as follows:
AT+cgdcont=1,"ip","cmnet"; +cgeqreq=1, 3, 64,384
ii. Cancel the rate limit by the command of AT
Set the rate to 0 by the AT command. That means not to apply specific rate. In this case,
the system will assign subscription rate only as possible.
AT+cgdcont=1,"ip","cmnet"; +cgeqreq=1, 3, 0, 0
6. Iub Bandwidth Limited (It is recommended to describe common problems like
bandwidth, alarm and configuration, which are not specific to DPA
independently.)
i. If the physical bandwidth of the Iub interface is limited, then the bandwidth of
AAL2PATH that can be obtained by HSDPA is small. As a result, the traffic
volume in the NodeB buffer area will be insufficient, and therefore the success
rate of the HS-SCCH will be low.
ii. If there are many R99 users in the cell, they will take the Iub bandwidth.
Therefore, the bandwidth of ALL2PATH that can be obtained by HSDPA will be
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Chapter 2 Data Analysis
49
small. Although the R99 ALL2PATH and the HSDPA ALL2PATH are configured
separately, they share the physical bandwidth. Thats why the success rate of the
HS-SCCH will be affected.
iii. Peak traffic flow of typical E1 configurations
At present, most operators adopt the ATM (E1) transmission. The following table
shows the theoretical peak throughput rate under different typical E1 transmission
configurations at the Iub interface. (Suppose that the total bandwidth configured for the
NodeB AAL5 is 384 kbps, and the transmission efficiency of the Iub interface is 75 %.)
Table 2-5 Theoretical Peak Throughput Rate under Different Typical E1 Configurations at the Iub Interface
E1 number Total
bandwidth
(Kbps)
AAL5
bandwidth
(Kbps)
AAL2
bandwidth
(Kbps)
Theoretical
maximum
transmission rate
(Kbps)
1 1920 384 1536 1152
2 3840 384 3456 2592
3 5760